1. Field of the Invention
The present invention relates to a method of producing a resin gear which is preferably used in a high load transmission system such as a power steering apparatus or the like.
2. Description of the Related Art
In conventional use, in order to assist steering force by an electric power steering apparatus, a worm wheel for transmitting drive force of a motor to the steering shaft is employed in a transmission system for transmitting drive force of a motor to the steering shaft.
As the worm wheel employed for the high load transmission system such as the power steering apparatus or the like, it is considered that a boss and an arm are constituted by an insert metal fitting for strength. A rim having teeth is constituted by a resin to silence the engaging sound.
In accordance with the conventional art, as described in Japanese Patent Application Laid-Open Publication (JP-A) No. 8-145146, a resin rim layer is formed on an outer periphery of an insert metal fitting from a gate of a metal mold. A gear cutting is applied to the outer peripheral surface of the resin rim layer so as to obtain a gear.
However, in accordance with the conventional art, after obtaining a blank material in which a gate forming portion is cut and removed from a product which is formed from a resin rim layer on an outer periphery of an insert metal fitting, a gear cutting is applied onto an outer peripheral surface of the resin rim layer of the blank material. Accordingly, it is necessary to remove burrs generated on the outer peripheral surface of the resin rim layer due to the gear cutting after applying the gear cutting.
An object of the present invention is to reduce a number of steps for producing a resin gear so as to reduce cost.
In accordance with the present invention, there is provided a method of producing a resin gear in which a resin rim layer is formed on an outer periphery of an insert metal fitting from a gate of a metal mold and a gear cutting is applied onto an outer peripheral surface of the rim layer so as to form a gear, comprising the steps of:
forming a gate forming portion on a side surface in a gate side of the resin rim layer and to at least an outer peripheral surface side;
applying a gear cutting having a gear cutting direction toward a side of the gate forming portion onto an outer periphery surface of the resin rim layer; and
thereafter cutting and removing the gate forming portion.